Heterodyning optical phase measuring device for specular surfaces

ABSTRACT

A system can include an axis, a motor coupled with the axis and configured to rotate the axis, an optical modulator coupled with the axis and configured to be rotated by the axis, a lens element, a projection surface, a laser device configured to shine light through the optical modulator to project structured light onto the projection surface through the lens element, and a sensor configured to capture an image of a sample and structured light that is reflected from the projection surface and the sample surface. The system can also include a computing system having a synchronization module configured to phase lock the system by coordinating the laser device and the sensor and an analysis module configured to compute a three-dimensional (3D) object based on the structured light that is reflected from the projection surface and the sample surface.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of, and claims priority to, U.S.patent application Ser. No. 16/451,567 filed Jun. 25, 2019, which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

Embodiments of the disclosed technology are generally directed tomethods, techniques, systems, and apparatuses for measuring specularsurfaces such as glass, plastic, and metal.

BACKGROUND

Certain conventional systems have used interferometry, laser scatteringmethods, or structured light for three-dimensional (3D) scanning toextract geometrical measurements, e.g., of a particular sample. Somestructured light measuring systems use a quasi-static projection oflight and analyze the subsequent captured images. A few of theseapproaches will analyze the bend or distortion in the line as a directmeasure of displacement, as well as the width of the projected lines asa measure of surface curvature.

In some cases, historical approaches will use a Fourier transform of thecaptured image to extract the spatial frequencies of the measuredsurface to enable surface reconstruction. In most all cases, thehistorical systems use multiple line widths and pitches in thestructured light to remove phase errors. However, many of theseapproaches could be considered static or unmodulated approaches and thussubject to higher background noise. Some of these approaches useshifting/moving light structure to enhance the signal but this istypically limited to a linear shift in one dimension.

Further, measurements of specular surfaces is a common industrialpractice in the manufacturing of glass (e.g., such as that used fordisplays), optics, automobiles, machined metallic parts, etc.Conventional techniques are typically optical in nature due to the speedof measurement over contact techniques. However, several challengesexist to be able to measure specular parts using non-contact opticaltechniques. Specifically, due to their specular surfaces, opticalmeasurements often will reflect the inhomogeneity of the light sourcebeing used; this may produce “hot spots” at specific angles ofobservation which undesirably result in saturation of thedetector/sensor, usually resulting in either data that is notprocessable or erroneous results. Further, some specular material isalso transparent, such as glass and or conventional optics, whichresults in very low signals reflected from the sample surface.Interferometers are often used to address the low signal levels andcustom part handling and illumination optics are employed to reduce theissues arising from inhomogeneity of the illumination. Consequently,this generally increases unwanted cost and time, while making the systemdesign more complicated

Embodiments according to the disclosed technology address these andother limitations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a first example of a measuring system in accordancewith certain implementations of the disclosed technology.

FIG. 2 illustrates a second example of a measuring system in accordancewith certain implementations of the disclosed technology.

FIG. 3 illustrates a first example of a method for generating andanalyzing data in accordance with certain implementations of thedisclosed technology.

FIG. 4 illustrates a second example of a method for generating andanalyzing data in accordance with certain implementations of thedisclosed technology.

FIG. 5 is a functional diagram 500 illustrating an example of ameasuring system in accordance with certain implementations of thedisclosed technology.

FIG. 6 illustrates a third example of a measuring system in accordancewith certain implementations of the disclosed technology.

FIG. 7 illustrates a fourth example of a measuring system in accordancewith certain implementations of the disclosed technology.

FIG. 8 illustrates an example of a method in accordance with certainimplementations of the disclosed technology.

DETAILED DESCRIPTION

Implementations of the disclosed technology generally pertain to methodsand apparatuses used for measuring the geometry of manufacturedproducts. Various industries typically rely on geometrical measurementsto ensure quality control and sound manufacturing practices of a productand, in some cases, these geometrical measurements are integrated intothe process flow to ensure that unit level specifications are met forpre-assemblies or integration, for example.

Certain implementations may include the combining of heterodyning phasemeasurements with one or more diffuse scattering screens to produce adiffuse light source. Alternatively or in addition thereto,implementations may include spatially modulating the diffuse lightsource while tracking the absolute phase of the modulation.Alternatively or in addition thereto, implementations may includeobserving the spatially modulated diffuse reflected light from aspecular object and reconstructing the optical phase projected acrossthe surface of the object.

Among the many advantages provided by the disclosed technology are theability to measure large area surfaces without mechanically moving theobject, the ability to measure very thin glass without concern ofinternal reflections, the ability to measure highly curved surfaces, anda low-cost solution for mass production, for example.

Semiconductor manufacturers may deposit/grow copper pillars or bumps onan integrated circuit as one of the last processing steps in thefactory. Control of the Bump Height and Bump Diameter are generallyconsidered critical process parameters to control due to the impact onyield and electrical properties if they are not processed correctly. Assuch, fully automated systems are needed to inspect and measure eachsilicon wafer and integrated circuit, as well as each bump on theintegrated circuit. Statistical sampling may be used to monitor thisprocess step and is typically considered a critical monitor for productreliability and yield.

Another rapidly growing market is the three-dimensional (3D) printer, oradditive manufacturing market, in which 3D objects are either designedfrom scratch or imaged in 3D and then reproduced. In the case of designfrom scratch, quality control of the 3D printed object can be monitoredusing geometric measurement tools to ensure the appropriatemanufacturing tolerance has been achieved. In the case of replication, asufficiently accurate shell, or equivalent surface, can be measured andsubsequently used to emulate the desired object, with the end userdefining the internal matrix under constraints of weight, strength,and/or function. These 3D print objects may be supplied to severalindustries including, but not limited to, aerospace, biomedical, orjewelry.

The disclosed technology generally provides methods and apparatuses forgenerating and projecting structured light on a sample and subsequentlymeasuring and analyzing the projected light to produce data in threedimensions. The structured light will typically consist of one or morelines of variable (i.e., controlled) width, pitch, and wavelength, whichwill cover a predefined area and be referred to herein as the LightFrame of Reference (LFOR). Within the LFOR there will be defined acentral axis, about which the LFOR may be rotated. One or more sensors,which may include, but not be limited to, a CCD array or camera, maymeasure the projected structured light on the sample at one or morelocations and be referred to herein as the image capture data array(ICDA). Images/data may be captured as the LFOR is rotated, thusgenerating an ICDA cube (ICDAC) of information. The data capture rateand the LFOR rotation rate may be synchronized such that sufficientinformation is captured to satisfy Nyquist's Theorem for both spatialand temporal sampling.

A specified area that may include, but not be limited to, a single pixelin the ICDA may be analyzed through the ICDAC which amounts to tracingthe information in this pre-defined area as a function of time and thuslight intensity modulation. A null condition generally exists in an areaabout the central axis and can be removed by translating the LFOR,generating multiple LFOR's offset from one another, translating thesample, or other approaches. For a flat surface, the spatial frequencieswill typically all be the same and therefore may be used, though notrequired to be used, as a reference signal for each trace through theICDAC.

A non-flat surface may contain multiple spatial frequencies, and thuswill distort the structured light along the curvature of the surface.The amount of distortion is generally related to the displacementperpendicular to the incoming light. As the LFOR is rotated, thedistortion manifests itself as a phase lag or lead in the ICDAC trace ascompared to the reference flat surface. The relative phase compared tothe reference for each trace in the ICDAC can be extracted throughseveral methods including, but not limited to, time differencing,Lissajous analysis, product methods, Fourier analysis, phase lockingmethods, etc.

Given the modulated nature of the apparatuses, low level signals can bedifferentiated from back ground noise by using several differenttechniques, including time and frequency-based filtering, lock-indetections schemes, or other. Additionally, the wavelength of the lightand the type of sensor can be adjusted to maximize not only the amountof reflected light but also the detector sensitivity to that wavelengthof light, for example.

FIG. 1 illustrates a first example of a measuring system 100 inaccordance with certain implementations of the disclosed technology. Inthe example, the system 100 includes a light source 120 capable ofgenerating rotating, structured light that is projected onto a samplearea 110. The structured light, as projected onto the sample area 110,may be measured by a first sensor 160. A second sensor may be used tomeasure the angular position of the structured light. The data from thefirst sensor 160 and the second sensor may be collected and passed to acomputing system 190. The computing system 190 will have the ability tosynchronize the angular position as measured by the second sensor withthe data acquired by the first sensor 160. The computing system 190 mayalso be configured to store and analyze data.

FIG. 2 illustrates a second example of a measuring system 200 inaccordance with certain implementations of the disclosed technology.Similar to the system 100 of FIG. 1, the system 200 includes a samplearea 210, a light source 220, a first sensor 260, and a computing system290. However, with regard to system 200, the projected structured lighthas been shown to be rotated to an arbitrary angle with its subsequentdata representation shown on the computing system 290. It will beappreciated that the structured light can be rotated to arbitrary,discrete angles or rotated continuously. Regardless, data from the firstsensor 260 and the second sensor may be synchronized.

FIG. 3 illustrates a first example of a method 300 for generating andanalyzing data in accordance with certain implementations of thedisclosed technology. In Step 1, the structured light (Light Frame ofReference, LFOR) is generated at certain angles, rotated, andsynchronized with the sensor. Data is collected (Image Capture DataArray Cube, ICDAC) for both the reference and the sample for each LFORand stored for processing in Step 2. This process can be repeated formultiple LFOR or terminated after a single comparison.

In Step 2, ICDAC Traces (at each X,Y location in the sensor) may beextracted from the stored IDAC for both reference and sample andanalyzed to extract the relative phase. The relative phase may be storedfor each ICDAC trace to generate a phase map for each LFOR. MultiplePhase Maps may be compared to identify any phase wrapping errors, andidentified errors may be corrected. Phase may be converted to 3D heightmap information based upon the LFOR reference calibration.

Steps 1 and 2 may be done sequentially or in parallel.

FIG. 4 illustrates a second example of a method 400 for generating andanalyzing data in accordance with certain implementations of thedisclosed technology. In this alternative approach, the reference andsample data may be collected and analyzed simultaneously. IDAC Traceanalysis for relative phase may be done through software or throughhardware.

FIG. 5 is a functional diagram 500 illustrating an example of ameasuring system in accordance with certain implementations of thedisclosed technology. The example includes a synchronization module andan illuminator module.

Certain implementations of the disclosed technology generally include alarge, diffusely scattering surface, e.g., to remove any hot spots oroptical non-uniformity from the light source. The size of this surfaceis typically directly proportional to the size and curvature of thesample, thus allowing all angles of the sample surface to be illuminatedsimultaneously, e.g., without any hot spots. The sample and theobserving sensor may be geometrically configured such that the sensormay image the diffusely scattered, spatially modulated light form thesample surface. This spatially modulated light can be transformed intophase and subsequently surface height.

A spatially modulated light source may be used, as well as a diffuselyreflecting screen (e.g., having a flat or curved surface). The screenmay be illuminated off axis. A sample may be staged with automation tomanipulate the sample (e.g., by rotation). A sensor (e.g., an area scancamera) may have optics to image the surface of the sample object. Thecamera and optics may be set up in such a way to observe the diffuselyreflected light form the sample surface. Data may be collected in afirst sample orientation, the sample may be rotated (e.g., at least 90degrees), and data may be collected again. The surface may bereconstructed from the phase measurements using known phase unwrappingalgorithms, for example.

FIG. 6 illustrates a third example 600 of a measuring system inaccordance with certain implementations of the disclosed technology. Thesystem 600 includes a sample positioning apparatus 610 configured toposition a sample 601. The sample positioning apparatus 610 may be arobot or other automated apparatus having one or more axis for picking,placing, and/or aligning the sample 601, for example. The system 600also includes a staging apparatus 620 that may have one or more axis forpositioning the sample 610 before and/or during the measurement. Thesystem 600 also includes a measurement apparatus 660 for measuringdimensions, topography, and characteristics of the sample 601, forexample. The system 600 also has a computing system 690 that may beconfigured to synchronize motion, measurement, and/or analysis, forexample.

FIG. 7 illustrates a fourth example 700 of a measuring system inaccordance with certain implementations of the disclosed technology. Thesystem 700 includes a sample positioning apparatus 710, at least onelight source 720, a motor 730, an optical modulator 735, a lens element740, a first sensor 760, and a computing system 790. The system 700 alsoincludes a projection surface 750 configured to receive projected light.The sample positioning apparatus 710 is generally configured to positiona sample 701.

In the example 700, the motor 730 is configured to rotate an axis andthe optical modulator 735 is coupled with the axis and configured to berotated by the axis. The motor may be a brushless direct drive motor, astepper motor, or a brush DC motor, for example, or any other suitabletype of motor. In certain embodiments, the motor 730 may be configuredto continuously rotate the axis such that the optical modulator 735 iscontinuously rotated by the axis.

The light source 720 is configured to shine light through the opticalmodulator 735 to project structured light onto the projection surface750 through the lens element 740. The light source 720 may haveprojection optics that are capable of generating and rotating structuredlight, for example. In certain embodiments, the light source 720 may beselected from a group consisting of the following: a light emittingdiode (LED), a laser, and a filament source.

In certain embodiments, the system has multiple light sources, includingthe light source 720, that are configured to eliminate any nullconditions. These multiple light sources may be configured to shinelight at different widths, spatial frequencies, and angle of incidenceto extend dynamic range or eliminate phase errors.

In certain embodiments, the optical modulator 735 includes an encoderthat is configured to cause a pattern to be created by the structuredlight that is shined by the light source 720 onto the projected surface750. The projection surface 750 may be made of a material, e.g., a roughmaterial, that is selected from a group consisting of the following:paper, metal, cardboard, cloth, fabric, and paint. The surface of thesample 701 may be shiny, e.g., the sample 701 may be made of glass.

In the example 700, an optical sensor apparatus includes at least thefirst sensor 760 and is configured to capture an image of the sample 701by diffused light that is reflected from the projection surface 750 andsubsequently reflected from the sample 701. The optical sensor apparatusmay include an array of more than one sensor selected from a groupconsisting of the following: a CMOS sensor, a photodetector, aphotomultiplier tube (PMT), and a charged coupled device (CCD). Thesurface of the sample 701 may act to distort or deflect the structuredlight, and the sensor 760 may read this distorted light, for example.

The computing system 790 includes a synchronization module that isconfigured to phase lock the system by coordinating at least one lightsource 720 and the first sensor 760 and any other associated sensors.The computing system 790 further includes an analysis module that isconfigured to compute a three-dimensional (3D) object based on thereceived diffuse light that is reflected from the projection surface 750and the sample 701. The features of the 3D object may be related to theamount of light distorted by the sample 701, for example.

In certain embodiments, the first sensor 760 may be coupled with thesample positioning apparatus 710, e.g., by way of a table. Inalternative implementations, the first sensor 760 may be physicallyseparate from the sample positioning apparatus 710.

In certain alternative implementations, the structured light that isprojected onto the projection surface 750 may be projected from behindthe projection surface 750 rather than from the front of the projectionsurface 750.

FIG. 8 illustrates an example of a computer-implement method 800 inaccordance with certain implementations of the disclosed technology. At802, a motor rotates an axis, causing an optical modulator that iscoupled with the axis to rotate. In certain embodiments, the motorcontinuously rotates the axis such that the optical modulator that iscoupled with the axis is continually rotated by the axis.

At 804, a light source shines light through the optical modulator toproject structured light onto a projection surface through a lenselement. The light source may include at least one selected from a groupconsisting of the following: a light emitting diode (LED), a laser, anda filament source. In certain embodiments, multiple light sources mayshine light at a number of different widths, spatial frequencies, andangle of incidence to extend dynamic range or eliminate phase errors.

At 806, an optical sensor apparatus having at least one sensor capturesan image of the sample and structured light that is reflected from theprojection surface and the sample surface, which may be shiny. Theprojection surface may be made of a material that is selected from agroup consisting of the following: paper, metal, cardboard, cloth,fabric, and paint, or any other suitable material.

In certain embodiments, the at least one sensor may be selected from agroup consisting of the following: a CMOS sensor, a photodetector, aphotomultiplier tube (PMT), and a charged coupled device (CCD).

At 808, an analysis module computes a three-dimensional (3D) objectbased at least in part on the structured light that is reflected fromthe projection surface and the sample surface.

While not illustrated by FIG. 8, it will be appreciated that the method800 further includes a synchronization module phase locking the systemby coordinating the light source and the at least one sensor.

The disclosed aspects may be implemented, in some cases, in hardware,firmware, software, or any combination thereof. The disclosed aspectsmay also be implemented as instructions carried by or stored on one ormore or non-transitory computer-readable media, which may be read andexecuted by one or more processors. Such instructions may be referred toas a computer program product. Computer-readable media, as discussedherein, means any media that can be accessed by a computing device. Byway of example, and not limitation, computer-readable media may comprisecomputer storage media and communication media.

Additionally, this written description makes reference to particularfeatures. It is to be understood that the disclosure in thisspecification includes all possible combinations of those particularfeatures. For example, where a particular feature is disclosed in thecontext of a particular aspect, that feature can also be used, to theextent possible, in the context of other aspects.

Also, when reference is made in this application to a method having twoor more defined steps or operations, the defined steps or operations canbe carried out in any order or simultaneously, unless the contextexcludes those possibilities.

Furthermore, the term “comprises” and its grammatical equivalents areused in this disclosure to mean that other components, features, steps,processes, operations, etc. are optionally present. For example, anarticle “comprising” or “which comprises” components A, B, and C cancontain only components A, B, and C, or it can contain components A, B,and C along with one or more other components.

Also, directions such as “right” and “left” are used for convenience andin reference to the diagrams provided in figures. But the disclosedsubject matter may have a number of orientations in actual use or indifferent implementations. Thus, a feature that is vertical, horizontal,to the right, or to the left in the figures may not have that sameorientation or direction in all implementations.

Having described and illustrated the principles of the invention withreference to illustrated embodiments, it will be recognized that theillustrated embodiments may be modified in arrangement and detailwithout departing from such principles, and may be combined in anydesired manner. And although the foregoing discussion has focused onparticular embodiments, other configurations are contemplated.

In particular, even though expressions such as “according to anembodiment of the invention” or the like are used herein, these phrasesare meant to generally reference embodiment possibilities, and are notintended to limit the invention to particular embodiment configurations.As used herein, these terms may reference the same or differentembodiments that are combinable into other embodiments.

Although specific embodiments of the invention have been illustrated anddescribed for purposes of illustration, it will be understood thatvarious modifications may be made without departing from the spirit andscope of the invention. Accordingly, the invention should not be limitedexcept as by the appended claims.

The invention claimed is:
 1. A system, comprising: an axis; a motorcoupled with the axis and configured to rotate the axis; an opticalmodulator coupled with the axis and configured to be rotated by theaxis; a lens element; a projection surface; a light source configured toshine light through the optical modulator to project structured lightonto the projection surface through the lens element, the structuredlight having one or more lines of variable width, pitch, and wavelength;a sensor configured to capture an image of a sample and structured lightthat is reflected from the projection surface and the sample surface,wherein the wavelength can be adjusted to maximize the reflected lightand sensitivity of the sensor to the wavelength; and a computing systemincluding: a synchronization module configured to phase lock the systemby coordinating the light source and the sensor; and an analysis moduleconfigured to compute a three-dimensional (3D) object based at least inpart on the structured light that is reflected from the projectionsurface and the sample surface.
 2. The system of claim 1, wherein themotor is configured to continuously rotate the axis such that theoptical modulator is continuously rotated by the axis.
 3. The system ofclaim 1, wherein the sensor includes at least one selected from a groupconsisting of the following: a CMOS sensor, a photodetector, aphotomultiplier tube (PMT), and a charged coupled device (CCD).
 4. Thesystem of claim 1, wherein the motor is a brushless direct drive motor,a stepper motor, or a brush DC motor.
 5. The system of claim 1, whereinthe projection surface is made of a material that is selected from agroup consisting of the following: paper, metal, cardboard, cloth,fabric, and paint.
 6. The system of claim 5, wherein the material isrough.
 7. The system of claim 1, wherein the sample surface is shiny. 8.The system of claim 7, wherein the sample is made of glass.
 9. One ormore fixed, non-transitory computer-readable media containinginstructions that, when executed by a processor, cause the processor toperform a computer-implemented method comprising: a motor rotating anaxis, causing an optical modulator coupled with the axis to rotate; alight source shining light through the optical modulator to projectstructured light onto a projection surface through a lens element, thestructured light having one or more lines of variable width, pitch, andwavelength; an optical sensor apparatus having at least one sensorcapturing an image of the sample and also the structured light that isreflected from the projection surface and subsequently the samplesurface, wherein the wavelength can be adjusted to maximize thereflected light and sensitivity of the optical sensor apparatus to thewavelength; a synchronization module phase locking the system bycoordinating the light source and the at least one sensor; and ananalysis module computing a three-dimensional (3D) object based at leastin part on the structured light that is reflected from the projectionsurface and the sample surface.
 10. A method, comprising: a motorrotating an axis, causing an optical modulator coupled with the axis torotate; a light source shining light through the optical modulator toproject structured light onto a projection surface through a lenselement, the structured light having one or more lines of variablewidth, pitch, and wavelength; an optical sensor apparatus having atleast one sensor capturing an image of the sample and structured lightthat is reflected from the projection surface and the sample surface,wherein the wavelength can be adjusted to maximize the reflected lightand sensitivity of the optical sensor apparatus to the wavelength; asynchronization module phase locking the system by coordinating thelight source and the at least one sensor; and an analysis modulecomputing a three-dimensional (3D) object based at least in part on thestructured light that is reflected from the projection surface and thesample surface.
 11. The method of claim 10, further comprising the motorcontinuously rotating the axis such that the optical modulator iscontinually rotated by the axis.
 12. The method of claim 10, wherein theat least one sensor is selected from a group consisting of thefollowing: a CMOS sensor, a photodetector, a photomultiplier tube (PMT),and a charged coupled device (CCD).
 13. The method of claim 10, whereinthe sample surface is shiny.
 14. The method of claim 10, wherein theprojection surface is made of a material that is selected from a groupconsisting of the following: paper, metal, cardboard, cloth, fabric, andpaint.
 15. The system of claim 1, wherein the light source is a plasmasource.
 16. The one or more fixed, non-transitory computer-readablemedia of claim 9, wherein the light source is a plasma source.
 17. Themethod of claim 10, wherein the light source is a plasma source.